Self-monitoring of blood glucose is important for people with diabetes to be aware of their usual glucose levels and use them for their treatment. Enzymes having glucose substrates are employed as sensors for blood glucose self-monitoring. Examples of such enzymes include glucose oxidase (EC 1.1.3.4). Glucose oxidase has the advantages of being highly specific to glucose and having high heat stability. For this reason, it has been used as an enzyme in blood glucose sensors. The first announcement of such properties goes back to as long as 40 years ago. In blood glucose sensors that utilize glucose oxidase, the blood glucose level is measured when electrons generated in the process of converting glucose to D-glucono-d-lactone by oxidization are conducted to an electrode via a mediator. However, glucose oxidase poses a problem in that it tends to transfer protons produced by the reaction to oxygen, causing dissolved oxygen to adversely affect the measured values.
To solve such a problem, for example, NAD(P) dependent glucose dehydrogenase (EC 1.1.1.47) or pyrroloquinoline quinone (hereinafter also referred to as “PQQ” in the specification) dependent glucose dehydrogenase (EC1.1.5.2 (former EC1.1.99.17)) is used as an enzyme in blood glucose sensors. They have the advantage of being free from the influence of dissolved oxygen. However, the former, i.e., NAD(P) dependent glucose dehydrogenase (hereinafter also referred to as “NADGDH” in the specification) has poor stability and is cumbersome, requiring the addition of a coenzyme. The latter, i.e., PQQ dependent glucose dehydrogenase (hereinafter also referred to as “PQQGDH” in the specification), has the drawbacks of having poor substrate specificity and reacting to saccharides other than glucose, such as maltose and lactose, thereby deteriorating the accuracy of the measurement values.
Further, Patent Document 1 discloses Aspergillus-flavin-bound glucose dehydrogenase (hereinafter also referred to as “FADGDH”). Since the activity of this enzyme on xylose is only 10% of that on glucose, in the case of measuring the blood glucose level of a person who is taking a xylose tolerance test, the accuracy of the measured value may be impaired. The enzyme has a residual activity ratio of about 89% after treatment at 50° C. for 15 minutes, thereby exhibiting good heat stability. Patent Document 2 discloses the gene sequence and amino acid sequence of the enzyme.
Patent Document 1 WO2004/058958
Patent Document 2 WO2006/101239